This invention relates to a process for separating gas mixtures such as hydrogen containing carbon dioxide and nitrogen impurities, by adiabatic pressure swing adsorption.
Adiabatic pressure swing adsorption processes of the type described in Batta U.S. Pat. No. 3,564,816 with four adsorbent beds and two pressure equalization stages are widely used for separating gas mixtures such as hydrogen with water, carbon dioxide, methan and carbon monoxide impurities, as for example produced in stream reforming of naphtha. In these processes at least one component is selectively adsorbed and in most instances the desired product is the unadsorbed effluent. By way of example, the Batta process is capable of yielding 99.9999% hydrogen product gas with no detectable quantities of the aforementioned impurities using four adsorbent beds each packed with an activated carbon first section and a crystalline calcium zeolite A second section.
The production rate of an adiabatic pressure swing adsorption system is of course limited by the capacity of the adsorbent beds for processing and separating the feed gas mixture. The bed capacity is limited by the maximum bed size which may be controlled by either the physical strength of the individual adsorbent particles or the permissable shipping size of adsorbent-containing vessels. It will be recognized that as-installed vessels are usually in the vertical position so that the bed height is limited by the adsorbent crushing strength.
One solution to this problem is to provide duplicate systems. By way of example, two sets of four bed systems may be used to increase an otherwise limited production rate. However, this is an expensive solution since the number of vessels is essentially doubled even if only slightly higher production is required.
An even more important limitation of prior art four bed systems is their percent recovery of hydrogen and relatively high required inventory of adsorbent.
A main object of this invention is to provide an adiabatic pressure swing adsorption process which affords higher percent recovery of unadsorbed product effluent than realized with prior art processes.
Another object is to provide an adiabatic pressure swing adsorption process which is not restricted in production rate by prior art limitations in adsorbent bed size.
Still another object is to provide an adiabatic pressure swing adsorption process which requires a smaller total volume of adsorbent vessels and a lower total quantity of adsorbent material than would be required by employing prior art systems.
Other objects of this invention will be apparent from the ensuing disclosure and appended claims.